Causes

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Amenorrhea can occur for a variety of reasons. Some are normal during the course of a woman's life, while others may be a side effect of medication or a sign of a medical problem.

Natural amenorrhea

During the normal course of your life, you may experience amenorrhea for natural reasons, such as:

Pregnancy

Breast-feeding

Menopause

Contraceptives

Some women who take birth control pills may not have periods. Even after stopping oral contraceptives, it may take some time before regular ovulation and menstruation return. Contraceptives that are injected or implanted also may cause amenorrhea, as can some types of intrauterine devices.

Medications

Certain medications can cause menstrual periods to stop, including some types of:

Antipsychotics

Cancer chemotherapy

Antidepressants

Blood pressure drugs

Allergy medications

Lifestyle factors

Sometimes lifestyle factors contribute to amenorrhea, for instance:

Low body weight. Excessively low body weight — about 10 percent under normal weight — interrupts many hormonal functions in your body, potentially halting ovulation. Women who have an eating disorder, such as anorexia or bulimia, often stop having periods because of these abnormal hormonal changes.

Excessive exercise. Women who participate in activities that require rigorous training, such as ballet, may find their menstrual cycles interrupted. Several factors combine to contribute to the loss of periods in athletes, including low body fat, stress and high energy expenditure.

Stress. Mental stress can temporarily alter the functioning of your hypothalamus — an area of your brain that controls the hormones that regulate your menstrual cycle. Ovulation and menstruation may stop as a result. Regular menstrual periods usually resume after your stress decreases.

Hormonal imbalance

Many types of medical problems can cause hormonal imbalance, including:

Polycystic ovary syndrome (PCOS). PCOS causes relatively high and sustained levels of hormones, rather than the fluctuating levels seen in the normal menstrual cycle.

Pituitary tumor. A noncancerous (benign) tumor in your pituitary gland can interfere with the hormonal regulation of menstruation.

Premature menopause. Menopause usually begins around age 50. But, for some women, the ovarian supply of eggs diminishes before age 40, and menstruation stops.

Structural problems

Problems with the sexual organs themselves also can cause amenorrhea. Examples include:

Uterine scarring. Asherman's syndrome, a condition in which scar tissue builds up in the lining of the uterus, can sometimes occur after a dilation and curettage (D&C), cesarean section or treatment for uterine fibroids. Uterine scarring prevents the normal buildup and shedding of the uterine lining.

Lack of reproductive organs. Sometimes problems arise during fetal development that lead to a girl being born without some major part of her reproductive system, such as her uterus, cervix or vagina. Because her reproductive system didn't develop normally, she can't have menstrual cycles.

Structural abnormality of the vagina. An obstruction of the vagina may prevent visible menstrual bleeding. A membrane or wall may be present in the vagina that blocks the outflow of blood from the uterus and cervix.

Ovulation is the release of an egg from one of the ovaries. It often happens about midway through the menstrual cycle, although the exact timing may vary.

In preparation for ovulation, the lining of the uterus, or endometrium, thickens.

The pituitary gland in the brain stimulates one of the ovaries to release an egg.

The wall of the ovarian follicle ruptures at the surface of the ovary. The egg is released.

Finger-like structures called fimbriae sweep the egg into the neighboring fallopian tube.

The egg travels through the fallopian tube, propelled in part by contractions in the fallopian tube walls.

Here in the fallopian tube, the egg may be fertilized by a sperm.

If the egg is fertilized, the egg and sperm unite to form a one-celled entity called a zygote.

As the zygote travels down the fallopian tube toward the uterus, it begins dividing rapidly to form a cluster of cells resembling a tiny raspberry.

When the zygote reaches the uterus, it implants in the lining of the uterus and pregnancy begins.

If the egg isn't fertilized, it's simply reabsorbed by the body — perhaps before it even reaches the uterus. About two weeks later, the lining of the uterus sheds through the vagina. This is known as menstruation.

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